Many non-butter spreads are known, in which it has been attempted to achieve the taste and spreadability of butter, but without its high saturated fat (and often also salt) content. Butter oil contains considerably more than 50% saturated fat.
Liquid vegetable oils such as rape, soya, sunflower and olive oils contain less saturated fat than butter oil. In spreads containing them, however, they are either hydrogenated or supplemented by (an often unspecified amount of) hydrogenated or other hard fats. According to Bailey's Industrial Oil Guide, the percentage of oil that has been transformed into trans-fatty acids in most margarine ranges between 20% and 40%.
Saturation or hydrogenation changes liquid oils into semi-solid materials that are spreadable. In particular, it allows a cheap oil to be turned into a semi-liquid, plastic or solid fat with particular properties of spreadability, shelf-life and texture. However, this hardening process, or the use of hard fats such as palm oil, makes it very difficult to produce a composition that can be spread easily under all likely conditions of use. The product is either too hard at refrigeration temperatures (0.degree.-5.degree. C.) or too soft at ambient temperatures (15.degree.-25.degree. C.).
Hydrogenation also destroys some of the nutritional value of a natural oil. Moreover, if hydrogenation is stopped before completion, when the desired degree of hardening has been achieved, the partially-hardened fats that are formed may be nutritionally more detrimental than fully hardened fats. The trans fatty acids that are formed by partial hydrogenation can cause very rapid increases in blood cholesterol and triglyceride levels. If the diet contains cholesterol, then the effect of trans fatty acids is increased. Further, since high triglyceride levels are associated with cardiovascular diseases, it will be readily appreciated that partial hydrogenation is potentially very dangerous.
It is a fact that the incidence of death from cancer (1 in 30 in 1900 to 1 in 5 in 1980) parallels the increase in consumption of hydrogenated vegetable oils. Cancers have been associated with poor diet. While statistics do not prove that trans and otherwise hydrogenated fatty acids cause cancer, consideration must be given to the vital functions of essential fatty acids which are interfered with by trans fatty acids.